The present invention relates to a motor driven portable circular saw, and more particularly, to a type thereof having an improved sawdust discharge arrangement.
One example of a conventional portable circular saw is shown in FIG. 1. The circular saw includes a housing frame 1 on which a hand grip portion 6 is integrally mounted for depressing and advancing the entire circular saw relative to a workpiece W (FIG. 2). In the housing frame 1, a drive motor (not shown) and a gear transmission mechanism (not shown) are accommodated. The gear transmission mechanism has an drive shaft on which a circular saw blade 2 is fixedly coupled. Thus, upon energization of the drive motor, the circular saw blade 2 is rotated about an axis of the drive shaft in a direction indicated by an arrow A through the gear transmission mechanism. An upper half portion of the circular saw blade 2 is covered with an upper blade guard 3 fixedly secured to the housing frame 1. The upper blade guard 3 has a semicircular shape and has a side web 3a formed with a sawdust discharge opening 4 through which sawdusts are discharged outside of the upper blade guide 3. The discharge opening 4 has an upstream end 4a and a downstream end 4b with respect to a flowing direction of the sawdusts. The upper blade guard 3 has anther side wall 3b (FIG. 3) confronting the one side wall 3a to provide a semicircular discharge passage 3c therebetween.
Further, a lower blade guard 7 is rotatably mounted on the drive shaft through a boss (not shown) for covering a lower half portion of the circular saw blade 2 during non-service state of the circular saw. The lower blade guard 7 has one side provided with an arcuate web 7a, and has another side provided with a sector plate (not shown) which is rotatably supported to the boss. The lower blade guard 7 is normally biased by a spring (not shown) toward its close position in a direction indicated by an arrow B. In such closed position, the lower blade guard 7 cooperates with the upper blade guard 3 to enclose substantially all the teeth of the circular saw blade 2. Incidentally, detailed arrangement of the lower blade guard is disclosed in U.S. Pat. No. 4,221,051.
For chopping the workpiece W, the drive motor is energized for rotating the circular saw blade 2 in the direction A, while an operator holds the hand grip portion 6. In this case, a front end of the lower blade guard 7 abuts the workpiece W and is pivotally moved toward open position against the biasing force of the spring in accordance with the forward motion of the housing frame 1, so that the lower blade guard 7 is gradually inserted into the upper blade guard 3. In this case, a sufficient space is provided between the upper blade guard 3 and the pivotally inserted lower blade guard 7 to provide the semicircular discharge passage 3c (FIG. 3) for example, a distance of 10 to 20 mm is provided between the upper and lower blade guards 3 and 7 when the lower blade guard 7 is positioned within the upper blade guard 3. Therefore, sawdusts upwardly urged by the circular saw blade 2 can pass through the circular passage 3c and along an inner peripheral surface of the upper blade guard 3, and are discharged outside through the dust opening 4 as shown in FIG. 2. The upper blade guard 3 has an arcuate end wall 3d contiguous with the discharge opening 4 for terminating the discharge passage 3c and for changing orientation of the sawdusts passing through the discharge passage 3c. Thus, the end wall 3 d is connected to the downstream end 4b of the discharge opening 4.
With this structure, most of the sawdusts discharged through the discharge opening 4 are not directed toward the operator but are laterally directed as shown by an arrow D in FIG. 3, since the discharge opening 4 is formed and opened at the side web portion 3a of the upper blade guard 3, and since the end wall 3d guide such travel of the sawdusts. However, several sawdust are directed toward the operator as shown by an arrow E due to uneven flowing modes of the sawdusts within the discharge passage. In other words, several sawdusts do not flow along the inner peripheral surface of the other side wall 3b of upper blade guard 3 nor along the end wall 3d, but the dusts are ejected toward the operator substantially linearly if the sawdusts do not undergo guiding by the end wall 3d. Thus the sawdusts flowing along the arrow E may degrade the chopping work. That is, the discharge opening 4 is formed in the upper blade guard 3 at relatively downstream side portion thereof for effectively discharging the sawdusts. Thus, the downstream position, i.e., the discharge opening 4 is positioned close to the operator. Consequently, the sawdusts passing along the locus E may easily splashes on the operator.